struct rusage usage;
getrusage(RUSAGE_SELF, &usage);
while (usage.ru_utime.tv_sec + usage.ru_stime.tv_sec + (usage.ru_utime.tv_usec + usage.ru_stime.tv_usec)/1000000.0 <= 20){
    getrusage(RUSAGE_SELF, &usage);
}
return;